Insight into photochemical oxidation of FENURON (cas 101-42-8) in water using iron oxide and oxalate: The roles of the dissolved oxygen

Add time:08/05/2019    Source:sciencedirect.com

The role of dissolved oxygen in the degradation and mineralization of FENURON (cas 101-42-8) in the photo-Fenton-like system by using a natural iron oxide and oxalate was studied in detail during this study; the natural iron oxide (NIO) α-Fe2O3 was used as an iron source at acidic pH. The dissolved oxygen concentration variation was followed during the process. The dissolved oxygen effect was elucidated by carrying out experiments in the presence and absence of oxygen. It was found that the degradation and mineralization rate were strongly affected by changes in the dissolved oxygen concentration. In the absence of oxygen, we noticed a slight degradation of fenuron (22% in 360 min); this degradation was caused only by the photo-reduction of Fe(III). Ferrous ions were continually generated in this way. Ferrous irons were not oxidized to Fe (III) because of the lack of dissolved oxygen. Moreover, no production of hydrogen peroxide was noticed. The mineralization rate depended strongly on the abundance of dissolved oxygen; fenuron was totally degraded in 120 min in an oxygenated system, in 150 min in a forced aerated system and in 180 min in a free aerated system. Dissolved oxygen permitted the production of species that influenced the degradation efficiency; it improved hydrogen peroxide production under irradiation. The superoxide ion can react with organic radicals leading to an opening ring reaction. The mass balance of the reactive species showed that dissolved oxygen was the main reactive consumed during the process. Acute toxicity of the fenuron degradation by-products was measured by a bioluminescence test on a Microtox 500 analyzer and the results were expressed as the percentage of inhibition of the luminescence emitted by the bacteria Vibrio fisheri. Bio-assays showed that the toxicity decreased with irradiation time which proved that the intermediates, generated during photo-oxidation by the photo-Fenton-like system by using NIO, are less toxic than fenuron.

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